Identification of patients who will benefit from a specific therapeutic procedure requires the accurate assessment of the severity of stenoses, their geometry and spatial orientation. Most therapeutic decisions are currently based on information obtained through digital subtraction angiography. Standard angiographic images are not providing sufficient information needed to make therapeutic decisions. The long-term goal of this four-year project is to continually develop cone beam CT angiography (CBCTA) imaging technique to provide useful three-dimensional (3D) vascular images needed for diagnostic and therapeutic decisions. Intravenous cone beam CT angiography (IV-CBCTA) combines cone beam CT imaging principles with those of intravenous digital angiography. IV-CBCTA requires only a single intravenous contrast injection and volume scan to provide a true 3D description of vascular anatomy and stenoses in head and neck. This IV-CBCTA imaging technique will be superior to conventional angiography and have a strong clinical impact because it will provide a direct, unambiguous and accurate 3D measurement of stenoses, aneurysms, and other irregularities and malformations, including caliber, geometry and spatial orientation, while reducing the invasiveness of the procedure, procedure time and total x-ray exposure. IV-CBCTA continues to be developed and validated through computer simulation, phantom, and animal studies performed on a rotational CBCTA imager that uses a flat panel detector. Specifically, the aims of the proposed research are: 1) to optimize the implementation of cone beam vascular reconstruction algorithms to achieve on-line reconstruction; 2) to develop the flat panel detector-based prototype imaging system for IV-CBCTA imaging 3) to perform phantom studies to validate the IV-CBCTA technique and optimize the system performance; and 4) to use the prototype imager for animal experiments as a prelude to human studies.